<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>
    <div class="box"></div>
    <style>
        /* 盒子样式 */
        .box {
            position: relative;
            width: 200px;
            height: 100px;
            background-color: pink;
            box-shadow: 0px 0px 10px rgba(0, 0, 0, 0.2);
        }

        .box:after {
            content: '';
            position: absolute;
            top: 0;
            right: 0;
            width: 0;
            height: 0;
            z-index: 99;
            border-left: 20px solid transparent;
            border-right: 20px solid rgba(0, 0, 0, 0.2);
            border-bottom: 20px solid transparent;
        }
    </style>
</body>

</html>